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Groups > comp.os.linux.development.apps > #387

Re: EOF, close(), shutdown(), on POSIX sockets

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On 2012-01-12, Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:
> Andrei Voropaev <avorop@mail.ru> writes:
>> Of course, many protocols allow sending of explicit notification to the peer
>> when more data is not going to be accepted. But even in this case you
>> should be ready to handle EPIPE error.
>
> You seem to be addressing the question of when the transmitter can know
> the receiver has shut down.  My experience has been that when the
> *transmitter* has shut down, the receiver may wait an arbitrary amount
> of time in a read() before finally returning a 0.

Only because of network issues. When the transmitter has sealed that
direction by shutting it down, it means that there is a queue of packets
on the transmit side which has to drain. Only the last segment will
carry the FIN flag indicating "I am the last". 

The network can be disrupted in the meanwhile.

(Basically no byte that is sent by the transmitter will reach the receiver
in a guaranteed time, and that includes the FIN flag.)

On a fast, reliable network, you should not be seeing delays in read
when the other side has shut down the connection.

If the transmitting host crashes, or there is a long-term network
outage or something else (e.g NAT mapping entry expiring, so you permanently
lose the virtual circuit with no notification), that is different.

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EOF, close(), shutdown(), on POSIX sockets David Dyer-Bennet <dd-b@dd-b.net> - 2012-01-05 17:17 -0600
  Re: EOF, close(), shutdown(), on POSIX sockets Kaz Kylheku <kaz@kylheku.com> - 2012-01-06 01:10 +0000
    Re: EOF, close(), shutdown(), on POSIX sockets David Dyer-Bennet <dd-b@dd-b.net> - 2012-01-06 09:59 -0600
  Re: EOF, close(), shutdown(), on POSIX sockets Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-01-05 21:20 -0700
    Re: EOF, close(), shutdown(), on POSIX sockets David Dyer-Bennet <dd-b@dd-b.net> - 2012-01-06 10:00 -0600
    Re: EOF, close(), shutdown(), on POSIX sockets Andrei Voropaev <avorop@mail.ru> - 2012-01-12 16:07 +0000
      Re: EOF, close(), shutdown(), on POSIX sockets Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-01-12 12:57 -0700
        Re: EOF, close(), shutdown(), on POSIX sockets Kaz Kylheku <kaz@kylheku.com> - 2012-01-12 20:04 +0000

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